The present invention relates to novel carrier systems based on organic phospholipids capable of forming bilayers in aqueous solution, amphoteric surfactants, and nonionic surfactants, wherein these carrier systems allow water-insoluble polymers to be incorporated into aqueous solutions.
Organic phospholipids play an important role in the cosmetics and pharmaceutical industries because of their outstanding physiological properties, such as, for example, emulsifying, softening, and anti-oxidant effects. When hydrolyzed, organic phospholipids yield phosphoric acid, an alcohol, a fatty acid, and a nitrogenous base. Most phospholipids are amphiphatic, i.e., have polar xe2x80x9cheadsxe2x80x9d and non-polar xe2x80x9ctails.xe2x80x9d As a result, most phospholipids tend to arrange spontaneously into a bilayer when suspended in an aqueous environment, with the polar heads contacting the water and the non-polar tails contacting each other. Most naturally occurring phospholipids prefer to form vesicular bilayers in water solutions. In such a bilayer vesicle, no non-polar part of the phospholipid has any contact with the water solution.
Because of their non-polar portions, phospholipids typically are water-insoluble and incompatible with many water soluble anionic compounds, such as anionic surfactants. While they can be solubilized in water at low levels by a range of surfactants, this is often not easily accomplished.
Instead, solubilization has been accomplished conventionally using specific solubilizing agents in aqueous alcoholic solutions. For example, U.S. Pat. No. 4,874,553 to Hager et al. discusses methods of rendering phospholipid mixtures water-soluble or water-dispersible by using certain amine compounds as solubilizing agents. U.S. Pat. No. 4,174,296 to Kass describes a method of improving the solubility of phospholipid compounds in water, in particular lecithin compounds, by mixing lecithin with specific single solubilizing agents, including amphoteric and anionic surfactants. These methods utilize alcohol for cosolubilization. Alcohol solutions can have the drawback of disrupting any bilayer formation by altering the solution such that the alcohol functions as a secondary solvent.
Lecithins and other phospholipids have been used in the pharmaceutical industry to formulate carriers for water-insoluble drugs. For instance, in U.S. Pat. No. 5,173,303 to Lau et al., water-insoluble material is encapsulated by vesicles composed of phospholipids such as lecithin. Ribosa et al., in xe2x80x9cPhysico-chemical modifications of liposome structures through interaction with surfactants,xe2x80x9d Int""l Journal of Cosmetic Science 14:131-149(1992), also discuss solubilization of phospholipids via the interaction of liposomes with surfactants. Lau and Ribosa, however, investigated only dilute solutions of pure liposomes.
Despite difficulties in solubilization, certain organic phospholipids, such as lecithin, can advantageously give hair and skin a soft, moisturized feel because they have a strong affinity for the hydrophobic surface of the hair and skin. In addition, these phospholipids are toxicologically safe. It would thus be desirable for cosmetic and pharmaceutical applications to provide delivery systems that include such organic phospholipids as a carrier for other lipophilic ingredients, without the need for alcohols and other similar solvents.
In addition to solubilizing lipophilic ingredients such as oils, vitamins, and ceramides in aqueous systems, it would be desirable to solubilize other water-insoluble ingredients, specifically unneutralized or partially neutralized polymers, resins, or latexes, in aqueous delivery systems. U.S. Pat. No. 5,391,368 to Gerstein teaches solubilization of a hair-styling polymer in a composition comprising an anionic surfactant and an amphoteric surfactant. According to Gerstein, it is the amphoteric surfactant which dissolves the water-insoluble styling polymer because the polymer is not soluble in the anionic surfactant alone.
Gerstein presents some problems, however. Many hair care and hair setting products are formulated at acidic pH because of a desire for such products to be compatible with the pH of the scalp and hair surface. Gerstein does not disclose a pH at which its system is formulated, but if the Gerstein system is acidified, the polymer will precipitate out of solution. In addition, the Gerstein system does not carry and there is no suggestion that it could carry any additional lipophilic ingredients in its mixture of anionic surfactant, amphoteric surfactant, and styling polymer. Further, Gerstein does not describe the incorporation of its styling polymer into any products other than the disclosed styling shampoo, nor does Gerstein suggest that such incorporation would be possible.
Thus, there remains a need for an aqueous delivery system that can solubilize water-insoluble materials in such a manner that they will not precipitate out of solution upon acidification, where the amount of deposition of water-insoluble material can be controlled, and where the system could carry other ingredients in addition to the water-insoluble ingredient. For example, it would be beneficial to have a system which incorporates water-insoluble materials into compositions containing other ingredients, such as dyeing and permanent wave compositions. The present invention provides such a delivery system.
In order to achieve these and other advantages, the present invention is drawn to a composition made up of at least one organic phospholipid capable of forming bilayers in aqueous solution, at least one amphoteric surfactant, at least one nonionic surfactant and at least one water-insoluble polymer comprising at least one aromatic monomeric residue, wherein the aromatic monomeric residue comprises at least one hydroxyl substituted aromatic group. The amphoteric surfactant and the nonionic surfactant are each present in an amount equal to or greater than the amount of the organic phospholipid. The phospholipid, amphoteric surfactant, and nonionic surfactant are present in a combined amount sufficient to allow at least one water-insoluble polymer to be incorporated into an aqueous solution. The water-insoluble polymers used in the invention contain at least one aromatic monomeric residue having at least one aromatic group substituted with at least one hydroxyl group.
In another embodiment, the present invention relates to an aqueous delivery system for water-insoluble materials. The delivery system (or xe2x80x9ccarrierxe2x80x9d) includes the above-described composition and an aqueous phase. The amphoteric surfactant and the nonionic surfactant are each present in an amount equal to or greater than the amount of the organic phospholipid. The organic phospholipid, the amphoteric surfactant, and the nonionic surfactant are present in a combined amount sufficient to allow the water-insoluble polymer comprising at least one aromatic monomeric residue, wherein the aromatic monomeric residue comprises at least one hydroxyl substituted aromatic group to be incorporated into or solubilized by the delivery system. The present invention is also drawn to a process for the preparation of an aqueous system comprising: (a) combining at least one organic phospholipid capable of forming bilayers in aqueous solution, at least one amphoteric surfactant, and at least one nonionic surfactant to form a mixture, (b) heating the mixture obtained in step (a), (c) adding an aqueous solution to form a diluted mixture, and (d) cooling the diluted mixture. The water-insoluble polymer comprising at least one aromatic monomeric residue can be incorporated in step (a).
Finally, in yet another embodiment, the present invention is drawn to a method for treating keratinous substances such as skin, hair, or eyelashes. First an aqueous solution is prepared containing at least one organic phospholipid capable of forming bilayers in aqueous solution; at least one amphoteric surfactant present in an amount equal to or greater than the amount of the organic phospholipid; at least one nonionic surfactant present in an amount by weight equal to or greater than the amount of the phospholipid; and at least one water-insoluble polymer comprising at least one aromatic monomeric residue, as described above. The phospholipid, amphoteric surfactant, and nonionic surfactant are present in a combined amount sufficient to allow the water-insoluble polymer comprising at least one aromatic monomeric residue to be incorporated into the aqueous solution. The aqueous solution is then applied to the keratinous substances.
Reference will now be made in detail to the present preferred embodiment(s) of the invention.